1. Field of the Invention
The present invention relates to a crude oil composition estimation method, an absorption process simulation method in an absorption and liquefaction system, a process simulation method in a recovery system, and a method of producing an absorption and liquefaction system.
2. Description of the Related Art
Conventionally, vapors emitted into the air, for example, in the process of transporting crude oil have been one of large emission sources of volatile organic compounds (VOC). As an approach to environmental problems and energy problems, there is a growing need for absorption and liquefaction systems that recover volatile organic compounds by absorbing and liquefying them with absorption oil. As an example of absorption and liquefaction systems, a technique as illustrated in FIG. 5 is known in which VOC-containing vapors are brought into countercurrent contact with absorption oil and thereby liquefied and recovered (for example, see U.S. Pat. No. 1,621,821). The technique has a room for improvement in efficiency of recovery of volatile organic compounds. As illustrated in FIG. 6, a technique for improving the recovery efficiency is known, in which the pressure swing adsorption (PSA) process using an adsorbent (activated carbon) that selectively adsorbs hydrocarbons is used simultaneously with absorption and liquefaction (for example, see U.S. Pat. No. 4,066,423). As illustrated in FIG. 7, a technique is known which additionally uses a gas separation membrane that allows hydrocarbons to selectively pass through (for example, see U.S. Pat. No. 4,772,295).
Absorption and liquefaction systems using crude oil as absorption oil are also known. To design such an absorption and liquefaction system, the material balance in the absorption and liquefaction system need to be simulated based on the composition of vapors (gas) and the composition of crude oil (liquid). Here, the composition refers to the included components and concentrations thereof. In the simulation, the composition after an absorption and liquefaction process is estimated by performing vapor-liquid equilibrium calculation based on the composition of vapors and the composition of crude oil. In order to obtain a precise simulation result, the accurate compositions of vapors and crude oil are required.
The analysis of compositions of crude oil, however, requires enormous time and effort because a number of components are included in crude oil. Moreover, the analysis result obtained with time and effort does not necessarily have high reproducibility.
The properties of crude oil are found in, for example, open data such as the HMC-4A database released by Hydrocarbon Management Committee (HMC) and the American Petroleum Institute (API) organized according to oil kinds and producing areas, released by oil-related companies. Some process simulators for simulating an absorption process have the function of creating a simulated composition (crude oil simulated composition creating function) using a component represented by the boiling point based on a distillation curve as a hypothetical component of crude oil. Thus, even when the composition is unknown, a series of process simulations can be done by creating a simulated composition with hypothetical components with a process simulator based on open data, and using the created simulated composition. The simulated composition, however, differs from the composition of actual chemical substance components (hydrocarbon components) and therefore has a room for improvement in precision when used in simulation. The reason for this is that vapor-liquid equilibrium calculation cannot be accurately performed because the composition of vapors includes actual chemical substance components whereas the composition of crude oil includes hypothetical components.
The inventors of the subject application have conducted detailed analysis and examination on vapor compositions of crude oil. The inventors have found that vapors of crude oil include similar components irrespective of producing areas and other factors. The inventors have examined light components that have a large effect on the absorption operation among the components included in crude oil. The inventors have found that any crude oil has almost the same light components. Based on the result of such analysis and examination, the inventors of the subject application have found that accurately knowing the concentration for each typical component (composition of crude oil) in a crude oil composition table leads to a simulation with high precision.
In the absorption operation, a large amount of crude oil is usually used for allowing plenty of absorption capability in order to recover a maximum amount of hydrocarbon components in vapors. Thus, the difference between the compositions of crude oil before and after absorption is found to be extremely small when analyzed in the liquid phase. It is therefore difficult to estimate the composition of crude oil from the result of analysis in the liquid phase. By contrast, in the vapor phase, the analysis of light components is easy and, in addition, there are significant changes in composition before and after absorption because most of hydrocarbon components are absorbed. As a result, the amount of each component absorbed can be grasped precisely. Based on these, the inventors of the subject application have found that the composition of crude oil can be estimated from the analyzed values of light components in the vapor phase in the process of hydrocarbon absorption from vapors with crude oil.
There is a need for a crude oil composition estimation method of estimating the composition of crude oil for achieving a precise simulation result, an absorption process simulation method in an absorption and liquefaction system, a process simulation method in a recovery system, and a method of producing an absorption and liquefaction system.